The instant application should be granted the priority dates of Dec. 17, 2008, the filing date of the corresponding German patent application 10 2008 062 381.4, as well as Dec. 11, 2009, the filing date of the International patent application PCT/EP2009/008863.
The present invention relates to a method for setting an automatic level control of the plow in longwall mining operations, in underground coal mining, equipped with a hydraulic shield support and with a face conveyor that guides the plow at a plow guide mechanism formed thereon, whereby the position of the face conveyor, including the plow guided thereon, can be changed in the exploitation direction by means of a boom control mechanism that is supported on the shield support, and, by means of the boom control mechanism, a control angle for setting the motion of the plow in the exploitation direction as a climbing motion, a dropping motion or a neutral motion can be set.
One problem with the automatic level control of plow strokes, not only in the exploitation direction but also in the extraction direction of the plow, is, for example, on the one hand establishing an adequately large face opening in order to ensure the passage of the longwall equipment, for example without collision between plow and shield support frames as the plow travels past, and on the other hand keeping the yield of waste rock during the extraction work as low as possible, and consequently limiting the extraction work as much as possible to the seam layer without also picking up too much country rock. The deposit data concerning the seam thickness, footwall and roof levels, and the presence of saddles and/or depressions not only in the exploitation direction but also in the direction of travel of the plow, that are available prior to the extraction are too imprecise in order to be able to base an automatic control of the plowing and extraction work, including maintaining the required target face height, thereon.
The plow, which is equipped with chisels, has a fixed cutting height, depending upon the settings, and a relatively low cutting depth in the order of magnitude of about 60 mm, so that in contrast to a drum shearing, the height of cutting is in any case not variable during a plow stroke along the face front. In plow strokes, a control of the level of the plow via a control cylinder that is disposed between the face conveyor, has a fixed guide for the plow, and the shield support frame connected thereto, is provided as a so-called boom control. By means of the inclination of the face conveyor in the exploitation direction, which can be changed with the aid of the boom control, it is thus possible in addition to a level-neutral control, to impart to the face conveyor, and hence to the plow guided thereon, a dropping motion in the exploitation direction, even during the extraction travel, in which the plow, by the cutting of its base chisels into the footwall, tips or tilts, or also a climbing motion, in which the plow carries out an ascending extraction.
In connection with the extraction work using the plow, it should be possible to maintain a defined face opening, whereby this face opening is defined by the distance between the top canopy and the floor skid of the respective shield support frame in the region of its travel path. In particular where the footwall layer changes, or where the footwall is soft, having a lesser hardness than does the coal that is to be extracted, the main thing is to maintain the target height of the face by means of a permanent monitoring and adaptation of the level control of the plow.
If the footwall is harder than is the seam that is to be included in the extraction, a level control of the plow is also possible according to the known method of the boundary layer plow at the footwall, according to which the hard footwall assumes a certain guide function for the plow. Within the framework of a method known for this purpose, a sensor that is carried along at the level of the base chisel of the plow determines whether the base chisel is cutting in country rock, in other words in the footwall, or in the coal. First of all, from a hardware standpoint this method is vulnerable because the pertaining sensor, and the associated evaluation computer, are installed in an extremely harsh environment in or on the plow, and hence are subjected to corresponding stresses or defects that occur. Furthermore, the mobility of the plow requires a supply of power to the hardware by battery, and a data transmission via radio by means of a plurality of transponders disposed in the face, whereby the radio conditions, especially in low-roofed faces having high amounts of ferromagnetic components of the longwall equipment, are very difficult to control. Furthermore, this method also suffers from uncertainty with respect to its information-giving capability, and also entails corresponding time delays with regard to a possibly required regulation, because information that is at least somewhat reliable regarding the material cut by the plow can be obtained only after a number of plow strokes, i.e., after a shield support frame passes by a number of times, generally approximately five times.
It is therefore an object of the present invention to provide a method of the aforementioned type according to which, in all operating states of the longwall mining operation, an automation of the plow and extraction work is possible with respect to producing a defined face opening and/or the guidance of the longwall operation on the footwall layer.